An air-filled endotracheal cuff seals the tracheal tube within the lumen of the trachea to prevent leak during inflation and to prevent entry of secretions from the upper airway into the trachea and lungs. Present-day endotracheal tubes feature an air inflation channel and small-bore tubing leading to the cuff and a so-called pilot balloon in the proximal segment of the inflation channel to provide external visible proof of the state of cuff inflation. However, current pilot balloons no longer provide this proof. Unfortunately, recently marketed cuffed endotracheal tubes have abandoned the original purpose of the pilot balloon by substituting a "miniature" polymer molded bulb which remains normally in expanded position at zero pressure. The walls of such polymer bulbs are inelastic and are too thick to collapse with cuff deflation and consequently fail to give any indication of the patient's ventilator has failed to inflate the lungs.
Therefore, the several purposes of this invention are to create a pressure-volume monitor to continuously indicate externally the status of inflation of the endotracheal cuff. Secondly, to utilize an elastomer for the balloon of the monitor whose thin walls are collapsible and expandable to provide an appreciable change in balloon size with changes in internal air pressure, thereby to result in a sensitive and obvious indication of both pressure and volume in the cuff system without the use of an overflow spill valve. Thirdly, it shall be the purpose of this invention to control the elastomer balloon wall thickness to insure the sensitive response in the appropriate and safe range of cuff pressure, giving obvious evidence of pressures above 15 centimeters of water, which is the critical cuff pressure above which tracheal injury results. Fourthly, the invention shall provide means for identifying a normal level of pressure and volume in the endotracheal cuff by direct inspection of balloon size in relation to the structure of the rigid cage which surrounds the balloon, such containment of the balloon by the cage serving subsequently as a visual reference to discover minute changes in balloon size as long as the patient's trachea remains intubated. Finally, the invention shall include means to alert nursing personnel by warning and alarm signals to the hazards related to either excess cuff pressure or leaking collapsed cuffs which may in turn result in failure of lung inflation by a mechanical respirator. Attainment of these several features results in a practical, inexpensive, durable, mechanical pressure-volume sensor which continually and conveniently reveals the safety and security of the state of inflation of the endotracheal cuff.
This invention replaces the contemporary pilot balloon of only 0.5 to 1.0 milliliter volume with a reliable pressure-volume monitor capable of continuous indication not only of the state of collapse or expansion of the endotracheal cuff but, more importantly, indicating accurately the level of pressure within the cuff, permitting early discovery by attending personnel of both leakage and excessively high cuff pressure before problems arise. The balloon wall of the monitor is an appropriately thin elastomer. The size of the balloon resembles that of the cuff itself, about 20 milliliter volume at 10 centimeters of water and 30 milliliter volume at 20 centimeters of water, this pressure-volume behavior being the basis for a sensitive indication of system pressure by virtue of the balloon just contacting the cage structure at 10 centimeters of water pressure and bulging through windows in the cage at 20 centimeters of water, therefore, the balloon is constructed of silicone or Kraton rather than PVC, or other inelastic polymers. Non-elastic properties of polymers fail to reveal over-expansion of cuffs. Thus, the contemporary "PVC pilot balloons" fail to reveal visible evidence of excessive harmful cuff pressures or of zero pressure. Thus, the pressure-volume monitor of this invention utilizes a balloon with a specific wall thickness such that 20 ml of air produces a characteristic internal pressure. For example, three different balloons of different wall thickness produce pressures of 10 cm of water, 50 cm of water and 200 mm of mercury when filled to occupy the same space within the cage. By attaching the monitoring balloon in series with the inflation channel and endotracheal cuff of any endotracheal tube, one may identify whether the cuff pressure is harmful or benign, and thereby avoid the serious complications arising when high lateral wall pressures are exerted against the wall of the trachea. These cited pressures unfortunately cover the range of cuff pressures typical of currently available cuffed endotracheal tubes cuffs, the latter two being harmful.
On the other hand, the safety of the tracheal seal, during lung inflation, dependent upon the integrity of the cuff, particularly in patients on mechanical ventilation, may be simply and routinely monitored by inspecting the system of this invention. Nursing personnel may visually inspect the monitor, may palpate with two fingers the balloon's pressure, or may be allerted by pressure sensitive switches in the monitor to a failure of the cuff system.
The foregoing and other objects and advantages of the invention will be set forth in or are apparent from the following description and drawings.